Electron tube and heater type cathode therefor



Jan. 11, 1949. F, WL R 2,459,086

ELECTRON TUBE AND HEATER TYPE CATHODE THEREFOR Filed April 16, 1948 FIG. I.

A 0 22 El Ennentor CARL E MILLER By V (ItZneg Patented Jan. 11, 1949 ELECTRON TUBE AND HEATER TYPE CATHODE THEREFOR Carl F. Miller, Summit, N. J assignor to National Union Radio Corporation, Orange, N. J a corporation of Delaware Application April 16, 1948, Serial No. 21,325

10 Claims. 1

This invention relates to electron tubes and more especially it relates to tubes of the indirectly heated-cathode kind.

A principal object of the invention relates to an electron tube having an improved heatercathode construction.

Another object is to provide an improved heater type electron-emitting cathode which can be readily designed for operation with heater voltages over a wide range.

Another object is to provide a heater type cathode which is of more rugged construction than those using heater wires of the coiled or filamentary type.

A feature cf the invention relates to a unipotential heater type cathode for electron tubes, wherein the heating element comprises a tubular ceramic body having its surface coated or otherwise provided with a conductive material to impart a predetermined resistance to the heating element.

Another feature relates to a uni-potential heated type cathode wherein the heater element is in the form of a tubular ceramic member having a predetermined electric resistivity or conductivity, and which is surrounded by a tubular metal cathode sleeve, the sleeve being capable of longitudinal expansion without buckling, when the heater member is raised to an emitting temperature.

A further feature relates to an electron discharge tube employing a novel construction of heater type cathode whereby the cathode is of rigid construction throughout, and is capable of being supported in very close spaced relation to a surrounding grid electrode, and while maintaining low leakage paths between the cathode and the said grid.

A further feature relates to the novel construction of a heater type cathode for electron discharge tubes whereby the cathode can be readily centered with respect to a surrounding grid or other electrode, and while permitting the cathode to expand longitudinally without changing its centered relation with respect to said surrounding electrode.

A still further feature relates to the novel organization, arrangement and relative location and interconnection of parts which cooperate to provide an improved electron discharge tube of the heater cathode type.

Other features and advantages not particularly enumerated, will be apparent after a consideration of the following detailed descriptions and. the appended claims.

In the drawing,

Fig. 1 is an elevational view, paftly sectional of an electron tube embodying features of the invention.

Fig. 2 is a cross-sectional view of Fig. 1, taken along the line 2-2 thereof and viewed in the direction of the arrows.

Merely for purposes of illustration and explanation, the invention is shown in the drawing as embodied in an electron discharge tube of the triode type. It will be understood of course, that the cathode unit which embodies features of the invention, can equally well be used in connection with any other well-known kind of electron tube whether of the diode 0r multi-grid kind. Furthermore, while the drawing shows a tube of the flattened glass header type, it will be understood that this is merely for purposes of explanation.

In the drawing, there is shown an enclosing envelope or bulb I, of glass or other suitable material which is sealed at its lower end to a flattened glass header 2, through which are sealed in a vacuum-tight manner the respective leadin members or plug-in prongs 3, 4, 5, 6, 1. Suitably supported within the bulb I, is an electron tube mount or assembly, comprising the heater element 8, the electron-emitting cathode element 9, the foraminous control grid [0 and the output plate of anode II. All these elements are held in predetermined concentric fixed relation by being mounted between upper and lower mica discs I2, l3, in the manner well understood in the electron tube art. Thus, merely for illustrative purposes, the anode ll may.have at its opposite edges lugs M, which pass through corresponding openings in the discs l2, l3, and bent over so as to join the plate H as a unit with the discs l2 and I3. The grid Ill may, for example, consist of a pair of so-called grid side rods l5, l6, around which is wound in helical fashion a fine grid wire H, the turns of which are welded or otherwise integrally united with the side rods l5, IS. The opposite ends of the side rods l5, l6, extend through corresponding openings in the discs l2 and I3, and if desired, the ends of these side rods may be peened or otherwise enlarged to restrict the longitudinal movement of the grid. The cathode consists of a tubular metal sleeve ill of nickel or other suitable metal, preferably, although not necessarily, of cylindrical shape, the outside diameter of this sleeve being less than the internal diameter of the grid l0 so as to provide the required predesigned circumferential spacing between the cathode sleeve and the said grid.

,ductive with an upwardly extending metal post or rod 2! which extends through a central opening in the disc i2. Metal disc it also has acentral downwardly extending arm 22 which is arranged to fit within a tubular ceramic sleeve 23. The arm 22 is arranged to be cemented within the upper end of sleeve 23 by any suitable electrically concement 24. Preferably, although not necessarily, the upper end of sleeve 23 abuts the disc l9. Likewise, cemented into the lower end of the sleeve 23 is a metal rod 25 which is cemented to the said sleeve by' electrically conductive cement 26, the rod 25 extending downwardly through a central opening in the disc 12. Located between the lower end of sleeve i8 and member 23 is an annular insulator disc or spacer ring 21 of ceramic or similar insulating material, the outer periphery of which is recessed and into which is crirnped the corresponding region 28 of the sleeve l8. Preferably, the ring 2'1 is a slide it on the member 23 so that when'the cathode sleeve !8 becomes heated, it is capable of expanding longitudinally with respect to the member 23 without causing buckling of the said sleeve 18 and while maintaining the concentric spaced relation between sleeve l8 and member 23.

In accordance with one feature of the invention, the ceramic sleeve 23 has either its internal surface, its external surface, or both, coated or impregnated throughout the entire mass of sleeve 23, with a conductive material such as carbon so as to impart to the member 23 a predetermined electrical resistance. The thickness or conductivity of the carbon coating on member 23 will of course be chosen in accordance with the heater voltage for which the tube is to be designed. It will be understood of course, that the invention is not necessarily limited to the manufacture of the member 23 as a ceramic tube with a con ductive coating. If desired, the conductive material'can be incorporated in the ceramic batch at the time the sleeve 23 is fabricated so as to impact the ;desired predetermined electrical resistance or conductivity to the sleeve. Furthermore, the invention is not limited to the use of a conductive material in the form of carbon since other well-known conductive material such as powdered metals or the like can be applied to, or incorporated in, the member 23, so as to impart to it a predetermined electrical conductivity. In fact; if desired, the member 23 itself can be made out of extruded or molded carbon or graphite of the required electri3al resistance. For the purpose of heating the member 8 to the required temperature, the rod 25 is welded at its lower end to the lead-in prong 4, Likewise, the rod 2! is connected by a suitable conductor (notshown) to the lead-in prong 5, the prongs i and being arranged for connection to a suitable source of heating currentinot shown) For the purpose of connecting 'the cathode 9 in circuit, there is welded to the lower 'end'of sleeve 8 a metal tab 29 which in turn is welded to the-'lea'din prong 6. In some cases, the tab 29 may be connected also to one side of the heater supply, for example by being welded either to the prong 4 or prong 6 internally of the tube. For the purpose of connecting the control grid it in circuit, the side rod i5, for example, can be connected by a suitable metal tab 38 to the lead-in prong 3. Likewise, the plate or anode i is connected in circuit by means of a suitable metal tab 3! which is connected to the lead-in prong i.

From the foregoing, it will be seen that the heater element 8 can be predesigned so as to operate at the required temperature by controlling the quantity of conductive material or carbon which is coated on its surface, so that tubes can be designed very readily to operate over a wide range of heater supply voltages without changing the physical size of the elements. Furthermore, the rods 2! and restrict the contact area between the cathode sleeve 9 and the grid, and since the ends of the cathode sleeve do not extend into contact with either disc 52 or disc 5 3, it possible to have an extremely low leakage path between the cathode sleeve and the control grid. In certain cases, it may be desirable to insulate the cathode sleeve 63 from the heater element 8. In that case, the disc H) can be made of a non-conductive material such as ceramic and centrally fastened to this disc is a rod correcourse being conductively in contact, as for example by conductive cement 25, with the mem ber 23.

While one particular embodiment has been dis closed herein, variuos changes and modifications may be made therein without departing from the spirit and scope of the invention.

What is claimed is: .7

l. A heater type cathode for electron tubes, comprising a heater element in the form of a rigid tubular body constituted of composite insulator and conductor materials, heater current supply members attached to opposite ends of said tubular body, a tubular metal sleeve surrounding said body in fixed circumferential spaced relation thereto, and a coating of electron-emissive material on the external surface of said sleeve.

2. A heater type cathode for electron tubes, comprising a heater element in the form of a rigid tubular body carrying a quantity of conductive material to impart a predetermined resistivity thereto, current supply members rigidly attached to opposite ends of said body, a tubular metal sleeve surrounding said body, means to maintain said sleeve in fixed circumferential spacing with respect to said body, and a coating of electron-emissive material on the external surface or" said sleeve.

3. A heater type cathode, comprising a heater element in the form of a rigid tubular ceramic body carrying a quantity of conductive material to impart a predetermined resistivity thereto, current supply members fitted into the opposite ends of said ceramic body, a tubular metal sleeve in fixed surrounding spaced relation to said body, and a coating of 'electron-emissive material on the external surface of said sleeve.

4. A heater type cathode, comprising a heater element in the form of a rigid tubular ceramic body having its surface coated with a conductive material to impart a predetermined resistivity thereto, current supply members conductively fitted into the: opposite ends of said ceramic body, a tubularmetal sleeve in fixed surrounding spaced relation to said body, and a coating of electron-emissive material on the external surface of said sleeve.

5. A heater type cathode, comprising a heater element in the form of a rigid tubular ceramic body having its surface coated with conductive carbon to impart a predetermined resistivity to said body, current supply conductors fitted into the opposite ends of said ceramic body, a tubular metal sleeve in fixed surrounding spaced relation to said body, and a coating of electron-emissive material on the external surface of said sleeve.

6. A heater type cathode, comprising a heater element in the form of a rigid tubular ceramic body having a predetermined electric conductivity to act as a heater when current is applied to opposite ends thereof, a tubular metal sleeve surrounding said body in spaced relation thereto, a disc shaped member fastened to one end of said sleeve, a conductive arm centrally carried by said disc shaped member and fitted into one end of said ceramic body to form an electric current supply connection thereto, and another conductive arm fitted into the opposite end of said ceramic body and forming another electric current supply connection thereto.

7. A heater type cathode, comprising a heater element in the form of a rigid tubular ceramic body having its surface coated with conductive carbon to impart a predetermined electric conductivity to said body to enable it to act as a heater when current is applied to opposite ends thereof, a metal disc having a centrally extending rod fitted into one end of said body, a tubular metal sleeve integrally united to the margin of said disc, an insulator ring located between the opposite end of said body and said sleeve to maintain a predetermined circumferential spaced relation between said body and sleeve while permitting said sleeve to expand longitudinally with respect to said body.

8. A heater type cathode according to claim 7, in which said disc has another central arm extending therefrom in a direction opposite to said first arm, and another current supply arm is 6 fitted within the opposite end of said ceramic body.

9. A heater type cathode, comprising a heater element in the form of a ceramic tube having its surface coated with carbon to impart to it a predetermined electric conductivity, current supply rods cemented into the opposite ends of said ceramic tube, a tubular metal sleeve surrounding said ceramic tube, a metal disc welded to one end of said sleeve and carrying integrally one of said current supply rods, an insulator ring located between the opposite end of said sleeve and the corresponding end of said ceramic tube, said ring being united to said sleeve for movement as a unit therewith but being slidable on said ceramic tube.

10. An electron tube, comprising an enclosing envelope, an electron tube mount within said envelope, said mount comprising a heater element in the form of a carbon coated ceramic tubular body, a metal disc having a central downwardly depending arm which is cemented into the upper end of said body and another arm which extends upwardly from said disc, a tubular metal sleeve having its upper end rigidly joined to the margin of said metal disc, an insulator ring located between the lower end of said sleeve and the lower end of said ceramic body, a current supply arm cemented into the lower end of said body, a coating of electron-emissive material on the external surface of said sleeve, at least one other eletrode surrounding said sleeve, upper and lower spacer discs of insulation, the upper disc having an opening to receive said upwardly extending arm to centralize said heater element and sleeve with respect to said electrode, and said lower disc also having an opening to receive said current supply arm to centralize said heater element and sleeve with respect to said electrode, said electrode also being anchored to said discs.

CARL F. MILLER.

No references cited. 

